$ B = \left[\begin{array}{rrr}1 & 0 & 0 \\ 0 & 0 & 2 \\ 2 & 2 & 0\end{array}\right]$ What is $ B^{-1}$ ?
Solution: $ = \left[\begin{array}{rrr}1 & 0 & 0 \\ -1 & 0 & \frac{1}{2} \\ 0 & \frac{1}{2} & 0\end{array}\right]$